As the use of neural stimulating electrodes has increased, more attention has been directed towards studying possible adverse side effects attendant to their use. This is especially true for applications which require chronic stimulation at high current densities. The risk of tissue damage, which is generally believed to be associated with the toxic species formed electrochemically at the electrode tissue interface, has been hindering the progress in neural stimulation. The objective of this proposed program is to develop highly selective "ion exchange type" stimulating electrodes suitable for the electrical stimulation of neural elements and thus contribute to the development of electrical devices for treatment of various neurological disorders. Specifically, we plan to prepare and characterize highly reversible electrodes which are capable of handling very high charge injection and current densities without exceeding their reversible potentials. We also plan to develop ion exchange membranes with high transfer numbers and electrical conductivities to enclose such reversible electrodes so that electrical charge can be injected without contaminating the physiological media. Our work will initially be concentrated on the silver/silver chloride reversible electrode and then extend to other reversible electrode systems including a novel approach involving the attachment of redox functional groups to a base electrode material and the use of conductive polymer electrodes. After successful long-term INVITRO testing, ion exchange membrane covered micro-stimulating electrodes will be fabricated and delivered to NIH-NINCDS in the form of completely finished micro-stimulating electrode assemblies for IN-VIVO testing.